1. Field of the Invention
The invention relates generally to the field of optical switching. More particularly, the invention relates to the design, fabrication, assembly and packaging of micro electro mechanical systems (MEMS) technology optomechanical switching cells, and Nxc3x97M matrix switches composed thereof.
2. Discussion of the Related Art
Optical switching plays a very important role in telecommunication networks, optical instrumentation, and optical signal processing systems. In telecommunication networks, fiber optic switches are used for network restoration, reconfiguration, and dynamic bandwidth allocation.
There are many different types of optical switches. In terms of the switching mechanism, optical switches can be divided into two general categories.
The first general category of optical switches employs a change of refractive index to perform optical switching. This first general category can be termed xe2x80x9celectro-optic switches.xe2x80x9d Actually, the refractive index change can be induced by electro-optic, thermal-optic, acousto-optic, or free-carrier effects. In the last of these examples, free carriers are generated by an electric charge introduced into a device, thereby causing a change in the material""s dipoles, which in turn changes the material""s index of refraction. Heretofore, the general category of electro-optic switches was generally employed in the case of coupled optical waveguides.
The second general category of optical switches employs physical motion of one, or more, optical elements to perform optical switching. In this way, a spatial displacement of a reflected beam is affected. This second general category can be termed xe2x80x9coptomechanical switches.xe2x80x9d
Optomechanical switches offer many advantages over electro-optic switches. Optomechanical switches have both lower insertion loss and lower crosstalk compared to electro-optic switches. Further, optomechanical switches have a high isolation between their ON and OFF states. Furthermore, optomechanical switches are bidirectional, and are independent of optical wavelength, polarization, and data modulation format. An optomechanical switch can be implemented either in a free-space approach or in a waveguide (e.g., optical fiber) approach. The free-space approach is more scalable, and offers lower coupling loss compared to the waveguide approach.
Macro-scale optomechanical switches employing external actuators are currently available. For example, conventional optomechanical switches are available from JDS, DiCon, AMP, and Hewlett Packard. However, one problem with this macro-scale optomechanical switch technology is that macro-scale optomechanical switches are bulky. Another problem with this technology is that macro-scale optomechanical switches require extensive manual assembly. Another problem with this technology is that the switching speed of macro-scale optomechanical switches is slow. For instance, the switching times for the currently commercially available optomechanical switches range from 10 milliseconds to several hundred milliseconds. An even more serious problem is that their switching times often depends on their specific switching path (i.e., how far is the distance from the next output port from the current output port). This variation of switching time as a function of spatial displacement is highly undesirable from a systems integration point of view. Therefore, what is needed is a solution that requires less bulk and less manual assembly, while simultaneously providing faster and more consistent switching speed.
Meanwhile, a number of different micromachining technologies have been developing. Micromachining offers many advantages for building optomechanical switches.
Micro electro mechanical systems (MEMS) technology is a micromachining technique that uses a batch processing technique. Micro electro mechanical systems technology is similar to semiconductor electronics fabrication except that the resulting devices possess mechanical functionality, as well as electronic and/or optical functionality.
Micro electro mechanical systems technology is currently used to fabricate movable microstructures and microactuators. The use of micro electro mechanical systems technology to fabricate optomechanical switches can significantly reduce the size, weight, and cost of the resulting optomechanical switches.
Micro electro mechanical systems technology includes bulk-micromachining and surface-micromachining techniques. Both bulk-micromachining and surface-micromachining have been applied to fabricate fiber optic switches.
Many optomechanical switches employ movable micromirrors. Although there are many possible configurations for the micromirrors, vertical micromirrors (i.e., the mirror surface is perpendicular to the substrate) offer many advantages from the architecture and packaging point of view. Using vertical micromirrors, a simple matrix switch with a regular two-dimensional array of switching cells can be realized. In more detail, the input and output fibers can be arranged in the same plane as the matrix substrate. Further, packaging is greatly simplified in this configuration.
Most of the vertical micromirrors reported in the literature have been fabricated by one of five methods. The first method is anisotropic chemical etching of (110) silicon wafer (using, e.g., KOH solution). The second method is deep reactive ion etching (DRIE). The third method is electroplating or the LIGA process. The fourth method is flip-up micromirrors with surface-micromachined microhinges. The fifth method is torsion mirrors.
Referring to the first method, anisotropic etching of (110) silicon substrate can produce an atomically smooth micromirror surface. However, a problem with the anisotropic etching method is that monolithic integration of the micromirrors with the microactuators is difficult. In an attempt to address this problem, external bulk actuators have been used. In another approach to addressing this problem, the micromirror substrate is simply glued to a micro flap actuator. However, this is not a manufacturable process. Therefore, what is also needed is a solution that facilitates integration of the micromirrors with the microactuators while simultaneously yielding a manufacturable process.
Referring to the second method, direct reactive ion etching can produce vertical micromirrors with straight sidewalls (with an aspect ratio of approximately 50:1). However, a problem with the direct reactive ion etching method is that the surface of the etched sidewalls tend to be rough. The Bosch DRIE process produces a periodic corrugation on the sidewalls due to alternating etching/coating process. The actuators of DRIE mirrors are usually limited to comb drive actuators, which have a limited travel distance. Therefore, what is also needed is a solution that provides a smooth mirror surface while simultaneously providing a large travel distance.
Referring to the third method, a problem with electroplated micromirrors is that they often may not have straight or vertical sidewalls. The LIGA process can produce high quality micromirrors, however, it requires expensive X-ray lithography. Further, integration with the actuators is a difficult issue for LIGA micromirrors. Therefore, what is also needed is a solution that provides an economical straight mirror surface while simultaneously facilitating the integration of the micromirrors with the microactuators.
Referring to both the fourth and fifth methods, the microhinged mirrors and torsion micromirrors are usually made of polysilicon plates. However, chemical-mechanical polishing (CMP) or other process is usually required to smooth the resulting mirror surface. This reduces the efficiency of the manufacturing process by significantly increasing the number of process steps. In addition, control of the mirror angle to within 0.5xc2x0 as required by large matrix switches is difficult to achieve with microhinged mirrors and torsion micromirrors. Therefore, what is also needed is a solution that provides manufacturing efficiency while simultaneously providing the required control of the mirror angle.
Heretofore, the requirements of less bulk, less manual assembly, faster and more consistent switching speed, integration with actuators, smoothness and straightness of the mirror surface, sufficient mirror travel distance, economy, manufacturing efficiency, and control of the mirror angle referred to above have not been fully met. What is needed is a solution that simultaneously addresses all of these requirements.
A primary object of the invention is to provide an approach to integrating optomechanical switching cell micromirrors and microactuators that can be implemented on an optomechanical switching matrix scale, or even on a wafer scale. Another primary object of the invention is to provide an approach to self-assembling optomechanical switching cell micromirrors and/or microactuators. Another primary object of the invention is to provide an approach to making optimechanical switching cell micromirrors tilt-insensitive. Another primary object of the invention is to provide a microactuated optomechanical switching cell. Another primary object of the invention is to provide an optomechanical matrix switch architecture for uniform fiber coupling loss. Another primary object of the invention is to provide input/output power monitoring for an optomechanical matrix switch. Another primary object of the invention is to provide an optomechanical matrix switch with integrated microlenses. Another primary object of the invention is to provide an optomechanical matrix switch with integrated wavelength division multiplexers and/or demultiplexers. Another primary object of the invention is to provide on-chip hermetic sealing for an optomechanical matrix switch. Another primary object of the invention is to provide an approach to aligning optomechanical matrix switches with optical fiber ribbons.
In accordance with these objects, there is a particular need for the invention. Thus, it is rendered possible to simultaneously satisfy the above-discussed requirements of less bulk, less manual assembly, faster and more consistent switching speed, integration with actuators, smoothness and straightness of the mirror surface, sufficient mirror travel distance, economy, manufacturing efficiency, and control of the mirror angle, which, in the case of the prior art, are mutual contradicting and cannot be simultaneously satisfied.
A first aspect of the invention is implemented in an embodiment that is based on a method of making an optomechanical matrix switch, comprising: joining a plurality of mirrors on a carrier to said plurality of actuators on a substrate; and removing said carrier from said plurality of mirrors so as to form a plurality of optomechanical switching cells on said substrate. A second aspect of the invention is implemented in an embodiment that is based on a method of making an optomechanical matrix switch, comprising: positioning a plurality of mirrors adjacent a plurality of actuators on a substrate; joining said plurality of mirrors to said plurality of actuators so as to form a plurality of optomechanical switching cells. A third aspect of the invention is implemented in an embodiment that is based on an optomechanical switching cell, comprising a tilt-insensitive mirror. A fourth aspect of the invention is implemented in an embodiment that is based on an optomechanical switching cell, comprising: an actuator positioned on a substrate; and a mirror coupled to said actuator. A fifth aspect of the invention is implemented in an embodiment that is based on an optomechanical matrix switch, comprising: a substrate; a plurality of optomechanical switching cells coupled to said substrate, each of said plurality of optomechanical switching cells coupled to said substrate, each of such plurality of optomechanical switching cells including a mirror and an actuator; and a switch architecture for uniform fiber coupling loss. A sixth aspect of the invention is implemented in an embodiment that is based on an optomechanical matrix switch, comprising: a substrate; a plurality of optomechanical switching cells coupled to said substrate, each of said plurality of optomechanical switching cells including a mirror and an actuator; and a means for input/output power monitoring. A seventh aspect of the invention is implemented in an embodiment that is based on an optomechanical matrix switch, comprising: a substrate; a plurality of optomechanical switching cells coupled to said substrate, each of said plurality of optomechanical switching cells including a mirror and an actuator; and a plurality of integrated microlenses coupled to said substrate. An eighth aspect of the invention is implemented in an embodiment that is based on an optomechanical matrix switch, comprising: a substrate; a plurality of optomechanical switching cells connected to said substrate, each of said plurality of optomechanical switching cells including a mirror and an actuator; and a plurality of integrated wavelength division devices coupled to said substrate. A ninth aspect of the invention is implemented in an embodiment that is based on an optomechanical matrix switch, comprising: a substrate; a plurality of optomechanical switching cells coupled to said substrate, each of said optomechanical switching cells including a mirror and an actuator; and a hermetic seal coupled to said substrate, said hermetic seal providing a substantially gas tight isolation of said plurality of optomechanical switching cells. A tenth aspect of the invention is implemented in an embodiment that is based on a method of aligning an optomechanical matrix switch with an optical waveguide, comprising: providing an optomechanical matrix switch on a positioning stage; providing an optical waveguide on a substrate; and positioning said optomechanical matrix switch by moving said positioning stage relative to said substrate.
These, and other, objects and aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such modifications.